Heating and welding system



June 21, 1949. J SLEPI'AN ET AL 2,473,915

HEATING AND WELDING SYSTEM I Filed June 21, 1941 6 Sheets-Sheet 1 I wmuzssEs: I INVENTORS Joseph $16 an and Alfred White.

June 1949- J. SLEPI AN ET AL 2,473,915

- HEATING AND WELDING sYs'rm Filed June 21, 1941 6 Shoots-Sheet 2 wnuzssss:

INYENTORS au Jose 725']? Ian and ATTOR .J'

June 21, 1949.. J..SLEPIA N ET AL 3 HEATING AND 'ELDINGSYSTEI Filed June 21, 1941 v e sheets-sheet 4 WlTNESSES: I INVENTORS Joseph Slepz'an and ,4 fr %.W/?ife.

' ATTOR Y June 21, 1949. SLEPIAN ET AL 2,473,915

HEATING AND WELDING SYSTEM Filed June 21, 1941 6 Sheets-Sheet 5 WITNESSES: v v INVENTORS- Joseph .S'Zepian and Alf/ 20 5 While June 21, 1949. J. SLEPIAN El Al. 2,473,915

HEATING AND WELDING SYSTEM Filed June 21, 1941 6 Sheets-Sheet 6 wmusssss: 32/ INVENTORS Joseph .S'Zepiarz and [4711 AlfredB mm.

" ATTOR Y I Patented lnno 21, 15a

HEATING AND WELDING SYSTEM Joseph Slepian, Pittsbur- Edgewood,

a, and Alfred B. White, Pa., assignors to Westinghouse Eleotric Corporation, East Pittsburgh, P h .poration of Pennsyi m. a

Application June 21. 1941, Serial No. 399,084

27 Claims.

Our invention relates, generally, to energy 1 translating systems, and it has reference; in particular to heating and welding systems.

It is an object of our invention to provide a simple, tractable, and eiiicient relatively high frequency welding or heating system which shall be inexpensive to construct.

Another object of our invention is to provide apparatus for-welding a material by supplying discrete impulses to the material during selected half periods of an alternating'current source.

A more general object of our invention is to provide apparatus of simple structure for supplying power to an inductive load circuit.

Another general obiectof our invention is to provide voltage responsive apparatus for supplying power to a load circuit.

A further general object of our invention is to provide apparatus for supplying oscillatory power to an inductive load circuit at spaced time intervals.

A still "lrther general object of our invention is to provide apparatus for transferring energy at a high rate from a source to a load without draining the energy from the sourceat an appreciable rate.

Still another general object of our invention is to provide simple, tractable, and inexpensive apparatus for supplying variable power to an inductive lead.

A specific object of our invention is to provide a spotor seam welder in which the welding current is oscillatory having a frequency substantially higher than commercial frequency.

Another specific object of our invention is to provide an interrupted spot welder of simple and inexpensive structure.

A further specific object of our invention is to provide a novel arrangement for controlling valve means, particularly of the igmtron type.

Still another specific object of our invention is to provide a welding system for resistance or arc welding having an inductive welding circuit in which the welding current shall be oscillatory and of a frequency substantially larger than the commercial frequency of 60 cycles per second.

Other objects will, in part, be obvious and will, in part, appear hereinafter.

In its broader aspects, our invention applies to an inductive load; specifically, it applies to an induction heater or a welder. In accordance with our invention, the load is connected to a condenser source of stored electrical energy, which is energized from a suitable source, in such manner as to discharge the condenser into the in-,

. 2 ductive load circuit at predetermined intervals.

Thus, a high energy impulse or a relatively high frequency oscillating current is produced in the load gircuit. The condenser is discharged through valve means which is set to conduct when the condenser voltage rea es a predetermined value.

In accordance with a further aspect of our invention the condenser may be discharged at spaced intervals as determined by preset peak values of condenser voltage which increase as the condenser is charged to the value at which the load current flows. The condenser may be charged relatively slowly. If the load circuit is such that the condenser-load network has a relatively high natural frequency the condenser may be discharged. into the load circuit rapidly so that the rate of energytransfer to the load is high while the rate of energy drain from the source is inappreciable.

Specifically, our invention is applicable to spot and seam welding. The charged condenser is, in

this case, discharged through the welding circuit at timed intervals and produces intermittent relatively high frequency oscillatory welding impulses or single current impulses. The charged condenser may be connected to the welder, or to any inductive load for that matter, at selected points in waves of the source potential or of the condenser potential and thus the welding current may be adapted precisely to the material to be welded. By proper adjustment of 'valve means in the charging or discharging circuit of the condenser the chargeand discharge of the condenser may be repeated for each weld and in this manner an interrupted spot welding system of simple structure may be produced.

The valve means in the condenser circuit may be controlled from the condenser potential through a low pressure voltage gap and a. control device having a relatively low impedance to current of the resonant frequency of the discharge circuit,

Briefly then, our invention involves an inductive load circuit such as a spot or seam welding circuit, or an induction heating circuit energized by means of relatively high frequency impulses from a condenser, which acts as a source of stored electrical energy. The condenser may be charged from a suitable source of direct or alternating current power through an impedance which prevents thesource from supplying an\ appreciable amount of power directly to the welding or heating circuit. The connection of the welding or heating circuit to the condenser may be controlled by valve means trodes ll. g

of the arc discharge type through a control circuit which renders the valve means conductive in accordance with predetertime of connection may be varied with respect to either the voltage wave of the source or of the condenser to vary the amount of the charge or any effect of the resulting high frequency discharge on the source. When the condenser is connected to the welding or inductive heatin circuit which is provided with sufiicient inductance to provide a natural circuit frequency which is relatively high, relatively high frequency oscillations are produced in the welding or heating circuit so that heat energy may be supplied to an article being heated or welded by means of the relatively high frequency current impulses.

For a more complete understanding of the nature and scope of our invention, reference may be had to the following detailed description, which is to be taken in connection with the accompanying drawings, in which:

' Figure 1 is a diagrammatic view of a welding system embodying features of the invention;

Fig. 2 is a diagrammatic view of an induction heating system embodying the principal features of the invention;

Fig. 3 is a diagrammatic view of a spot or seam welding system embodying a modification of the invention;

Fig. 4 is a diagrammatic view of an induction heating system embodying a modification of the invention; m

Fig. 5 is a diagrammatic view of a spot or seam welding system embodying another modification of the invention; I v

Fig. 6 shows curves illustrating the operation of the welding systems shown in Fig. 5; v

Fig. '7 is'a diagrammatic view of a welding system illustrating a further modification of the invention;

' mined conditions of the condenser voltage. The

plied by the source 1. so as to prevent it from supplying electrical energy directly to the primary winding ll of the transformer II at any appreciable rate when it is connected to the condenser l'l.

With a view to providing for connecting the primary winding ll of the transformer I! to the condenser l'l under predetermine conditions to provide a discharge circuit therefor, valve means may be provided, such as, for example, the arc discharge device or valve 20. The valve may Fig. '8 is a diagrammatic view of a spot or seam welding system embodying the principal features of the invention;

Fig. 9 is a diagrammatic view of a welding system embodying a yet further modification of the invention;

be of any suitable type, being, for example, provided with an anode 2|, a mercury pool cathode 22, and a control electrodr. or igniter 23 positioned within a suitable casing 24 in a manner well known in the art.

In order 'to provide for applying a control voltage to the control electrode or igniter 23 to render the valve 20 conductive under predetermined conditions, suitable control means, such as the gaseous discharge device 2!, may be utilized. The gaseous discharge device may be of any suitable type comprising. for example, a cathode 21 which may be heated by connection to any suitable source of electrical energy, an anode 28 and a control grid 28.

With a view to rendering the gaseous discharge device non-conductiveuntil the charge on the condenser I'I reaches a predetermined value, suitable means may be provided for applying a negative bias voltage to the control grid 28 until such time as the charge of'the condenser i1 reaches the predetermined value. Since the charging current through the impedance is will be reduced to substantially zero as the charge of the condenser ll reaches a maximum, a voltage potentiometer It may be connected across the impedance l9 to'provide the desired negative bias voltage on the control grid as. A protective grid resistor Il may be provided to limit the grid curren When th'e c'ondenser I1 is initially connected to the generator II, the drop across the impedance I! is relatively high due to the fiow of A5 charging current therethrough, and as a result,

Figs. 10 and 11 show voltage curvesillustrating I' the operation of the welding system of Fig. 9;

Fig. 12 illustrates diagrammatically still an other modification of the invention embodied in awelding system;

a relatively high negative bias voltage is applied to the grid 28 of thelgaseous discharge device 25 from the potentiometer 30. The gaseous discharge device 25 is thus rendered non-conductive,

v so that the arc discharge device 20 efiectively.

' disconnects the primary winding It of the weld- Fig. 13 shows voltage curves illustrating the 1 operation of the system shown -in liig 'iil; and Fig. 14 is a diagrammatic-view o'f 'an induction' heating system embodyinggawetfurther modification of the invention Referring tov Figure 1 of the drawings, the

reference numeral Ill may denote, generally, a

welding clrcuit'wherein a welding transformer I2 is utilized to supply arelatively low voltage welding. current through the secondary winding It to work-ll which is positioned between the elec- In-order to supply a relatively large amount of electrical energy to the primary winding ii of the transformer l2 during a relatively short interval, suitable means, such as the condenser ll, may be provided. The condenser I'l may be energized from any suitable source .of electrical energy such as, for example, the direct current generator II.,- An impedance ll may be connected' in series circuit relation with generator ll andthe condenser II to limit the current suping transformer "from the condenser l'|.- As soon as the charge on the condenser l1 reaches a predetermined value, the voltage drop across the impedance is is reduced to. a predetermined value, so that the negative bias voltage on the control grid 28 is reduced sufiiciently to render t e gaseous discharge device 25 conductive.

An energizing circuit for the igniter 23 is thus provided from the positive terminal of the condenser I1 through the conductor 32, the primary winding I8 of the welding transformer II, the gaseous dischargev device 25, the igniter 23, mercury cathode 22 and conductor 33 to the negative terminal of the condenser.

The are discharge device 20 is thus rendered conductive, permitting the condenser H to discharge through the primary winding i6 oi the welding transformer so as to produce a relatively vice 2l is reduced to the arc drop between cycle hereinbefore described.

former may be determined source I 8.

anode 2| and cathode 22 of the are discharge device 20. -As soon as the condenser I1 begins to discharge, current commences to flow through the impedance II. from the source I. and a negative bias voltage from the impedance." is automatically appliedto the control grid 2| through 30. so that the gaseous discharge device 23 becomes non-conductive.

the potentiometer igniter 23 of the arc. discharge device isdeenergized. and current continues to flowv through the arc discharge device until the current drops-toa value below the predetermined minimum required to maintain the device conductive, when it ceases to conduct. The primary winding ii valves or are of the welding transformer l2is disconnected from the condenser l1, which may then recharge from the generator source i3 so. as to repeate the tend to flow from the source 13 through the arc discharge device, the reverse current oscillation from the condenser l1 will oppose this tendency and permit the device to becom non-conductive.

Since the inductance of the welding transby characteristics of the transformer. and suflicient inductance may not be provided by the transformer alone to produce a discharge circuit for the condenser i1 having the desired natural frequency, an external inductance 33 maybe inserted in the discharge circuit of the condenser to produce the desired characteristics in, the circuit. The condenser may thus be charged over a relatively long interva1 and discharged during a relatively short interval. Relatively steep wave front current waves may thus be produced to supply relatively large amounts of electrical energy to the welding circuit out effecting a serious drain of energy from the Should current in relatively short intervals, with- Referring to Fig. 2, it will be seen that an induction heating furnace 33 comprising an induction coil 31 and a cupola 33 for receiving a charge to be heated may comprise the discharge circuit of the condenser l1 instead of the welding transformer i2, as shown in Fig. 1. Th condenser I1 may be connected to the source It through to that shown and described in connection with Fig. 1 of the drawings.

Instead of utilizing a single arc discharge valve or device 20 and associated gaseous discharge device 25 for connecting the discharge circuit,

including the induction heating furnace to the condenser for single periodic impulses of electrical energy, an additional valve or are discharge device 40 having an anode 4|, mercury p001 cathode 42'and igniter 43 may be provided. The two valves or are discharge devices 20 and 40 are, in this instance, connected in the well known anti-parallel, back-to-back, or inverse relation so as to provide for conducting current from the condenser l1 through the circuit of the induction coil 31 in'both directions, instead of in one direction only as in Fig. l. The condenser may then 'be arranged to discharge in opposite directions through the induction coil and set up relatively high frequency oscillations therein.

A gaseous discharge device 25 may be utilized for applying a control voltage to the igniter 23 of the valve or are discharge device 20 to initially render it conductive, in a manner similar to that described in connection with Fig. 1. In order to provide for rendering the valves or are discharge devices 20 and 40 selectively conductive an impedance is in a manner similar charge circuit through the igniters eh'frequencyoeciiiaby the alternate dischargeubs'equently,-to.permit tions to be produced ing and char :of the condenser l1 .through the auxiliary inductance a,

suitable means maybe provided for supplyingcurrent oscillations in the discharge circuit are in reverse directions to that for which, their respective devices conduct, rectifier devices 43 and 41 maybe provided to protect the igniters.

1 When the condenser l1'is'initially'connected to the generator llfor charging,

a negative bias voltage is applied to the control grid 23 .of the gaseous discharge device 23 from thepotentiometer 30 because of the voltage drop across the impedancei3 caused by the charging current. when the'charge on the condenser I 1 reaches a predetermined value, the voltage drop across the impedance I3 is reduced to a predetermined value, so'that the negative bias voltage applied to the control grid 23 is reduced sufllciently to render the gaseous discharge device 26 conductive. Voltage is ,then appliedfrom the condenser l1 to the igniter 23 through the circuit extending from the positive terminal of the condenser l1, conductor 32, the induction coil 31, auxiliary inductance 35, conductor 43, conductor 50, anode 26 and cathode 21, of the gaseous discharge device 25, igniter 23 and mercury pool cathode 22 of the arc discharge device 20, and conductor 33 to the negative side of the condenser. The are discharge device 20' is rendered conductive, and the condenser l1 discharges through the induction coil 31, auxiliary inductance 35, conductor 49, are discharge device 20, and conductor 33, to the other terminal of the condenser H.

The condenser is thus charged in the opposite direction and the arc in ignitron 20 extinguishes. The auxiliary condenser 43, which is connected between the igniters 23 and 43 provides a relatively low impedance for the sharp wave front potential impressed from the condenser I1 after the arc extinguishes in the arc discharge device 20. What happens here is that a potential suddenly appears across the condenser 45 when ignitron 20 becomes non-conductive. The latter event occurs when the capacitor ,I1 is charged to its maximum potential and constitutes the only potential source in the network l1 33 2050493531 32. At the instant when the ignitron 20 becomes non-conductive the whole capacity potential is impressed across the anode and cathode of the ignitron (since the ignitron anode-cathode capacity is-small). The anode is connected to one terminal of condenser 45 and the cathode to the other.

A relatively sharp impulse of exciting current isthus applied to the igniter 43 through the circuit extending from the now positive terminal of the condenser l1 through the conductor 33, rectifier device 41, conductor 52, auxiliary condenser 45, conductor 53, rectifier device 46, lgniter 43, mercury pool cathode 42, conductor 49, auxiliary inductance 3i, induction coil 31 and conductor '32 to the other terminal of the condenser The are discharge device 4|! is thus rendered conductive, and the condenser l1 redischarges through the induction coil 31 in the enact-s reverse direction through the circuit extendin from the conductor a, conductor 84, are dischargedevice 40, conductorll, auxiliary inductance 8|, induction coil 31, and conductor 3! to the other terminal of the condenser l1.

Due to the absorption of electrical energy in heating the work in the cupola SI and overcoming the impedance of the discharge circuit, the amplitude of the oscillations of the relativel high frequency current in the'discharge circuit may gradually reduce. If no provision is madeior balancing the rate of supply of electrical energy to the condenser I] from the source ll against the rate of energy absorption in the discharge circuit, periodic oscillatory discharges of the condenser may result. The condenser ll under these conditions continues to discharge in opposite directions, at a relatively high frequency once the discharge of the condenser is initiated, until the voltage across the condenser is reduced to such a value that the high frequency current provided to the igniters 23 and 43 through the auxiliary condenser 45 becomes insumcien't to render the valves 20 and 40 conductive. Under these conditions, valves 20 and to become nonconductive and the condenser I'I isdisconnected from the induction coil 31 so that it may be recharged from the generator source ii. The sequence will be repeated when the voltage or the condenser II against reaches the predetermined value at which the negative bias voltage on the grid of the gaseous discharge device 28 is reduced sumciently to render the device conductive.

By properly balancing the rate of energy input from the generator source it through adjusting the impedance is with the rate of energy absorption in the discharge circuit including the induction winding 31, sustained oscillations of "relatively high frequency may be maintained in the discharge circuit.

Referring to Fig. 3, the reference numeral Il may denote conductors connected to a source of alternating current. Valve means of any suitable type, such as the rectifier device 58, may 45 be connected between the conductors II and the condenser il in series circuit relation with a variable impedance I51 for controlling the charging rate of the condenser. The primary winding conductive and the condenser therethrough and through the primary winding 8 ll'and ll in parallel relation to the auxiliary condenser ll.

When the voltage across the condenser II reaches a predetermined value, the low pressure gap 60 breaks down, since it is connected across the condenser I! through the circuit extending from the positive terminal of the condenser through the conductor 82, the primary winding ll of the welding -transformer II. the auxiliary inductance ll, conductor ll, rectifier device ll, resistor 84, low pressure gap 00, rectifier device ll, igniter l3 and conductor I0 to the negative terminal of the condenser.

The are discharge device 40 is thus rendered ll discharges ll of the welding transformer inducing an impulse of welding current in the secondary winding ll, charging the condenser l'l in the opposite direction to which it was originally charged. Since the auxiliary condenser provides a relatively low impedance path for the sharp wave front potential, which abruptly appears across the condenser ll when the arc extinguishes, the igniter 23 of the valve or are discharge device 20 supplied thereto through the auxiliary condenser 45 and the circuit described in connection with Fig. 2. The valve or are discharge device 20 becomes conductive and the condenser ll discharges again through the primary winding ll,

' this time through the arc discharge device 20,

recharging again in the original direction. Successive relatively high frequency impulses of electrical energy may thus be provided in opposite directions in a relatively short period through the primary winding it of the welding transformer I! to induce relatively high frequency welding currents in the secondary winding ll thereof for welding the work it positioned between the electrodes ii. I

The valves 20 and 40 may also be supplied with firing current repeatedly through the gap ll rather than through the capacitor 45. For this purpose the gap must be properly selected. In the event that the firing of the valves is through the gap the capacitor I! may be omitted.

In the Fig. 3 embodiment the capacitor II may also be supplied directly from the source rather l of the welding tran former u may be com than through a rectifier (58). This modification nected to the condenser II by valves or arc discharge devices 20 and 40 connected in inverse relation in a similar manner to that described in connection with Fig. 2.

Instead of utilizing a gaseous discharge device '55 of the type shown in Fig. 2 for initiating the conductivity of the valves or are discharge devices in response to predetermined conditions of condenser voltage, means such as the low pressure gap 60, such as is disclosed in Patent No. 2,326,074 6 to Joseph Slepian, dated August 3, 1943 and assigned to Westinghouse Electric 8: Manufacturing Company, may be used. The gap 60 may also be an open air spark gap. The gap 60 may be of any suitable type such as, for example, has

been developed for the protection of capacitors installed on transmission lines. For example, the gap may comprise a pair ofspaced electrodes ll positioned in predetermined relation within a casing 82, wherein the pressure may be reduced to a relatively low value so as to permit a glow discharge between the electrodes when a relatively low voltage of a predetermined value is applied thereto. The low pressure gap Oil may,

for example, be connected between the igniters ll source and providing an oscillatory charging cirof our invention is particularly useful in cases. in which the capacitor 45 is not used and the load decrement is such that the reversed potential impressed on the condenser I! after the first discharge of the condenser is insuflicient to break down the gap 60. In such an event a single impulse iiows through one of the valves 20 or ill during each half period 01' the source Bl. During the succeeding half period the condenser I1, hav- 0 ing been discharged, is recharged to the opposite polarity and discharges through the other valve (40 or 20). In this modification t e constants of the load circuit should be such that the energy stored in the condenser ll during each charging operation is substantially completely absorbed during the discharging operation so that the inverse potential impressed on the capacitor i1 during the discharging operation is relatively small.

Referring to Fig. 4, it will be seen that the condenser ll may be connected to a source of alternating current by means of conductors 55. An impedance may be provided for limiting the charging current to the condenser from the cuit therefor, such as, for example,'the resistor 88 and inductance 68. A resistor and an inductance 'Il may be utilized in the discharge circuit tocontrol the amplitude and frequency of the oscillations produced therein by discharging the condenser l'l therein.

Induction heating apparatus 38 comprising, for example, an induction coil 31 and a cupola 38 positioned therein for receiving a charge to be melted, may be connected to the condenser I! by valve means 12.

Instead of utilizing as valve means independent arc discharge devices of the type hereinbefore described in connection with Figs. 1 through 3, wepropose to combine the arc discharge devices into a single valve device of the arc discharge type having, for example, an, inverted U-shaped casing 13 with mercury pools 14 and 15 at the lower ends of the legs which function as anodes and cathodes alternately. depending on the instantaneous polarity of the applied voltage, and control electrodes or igniters l6 and I1, respectively. A small quantity of a foreign gas such as argon may be introduced into the casing to insure quick pick up when the mercury vapor pressure is low.

In order to provide for initiating operation of the valve means 12 and maintaining it conductive thereafter, suitable means such as, for example, the low pressure discharge gap 68 may be provided. Rectifier devices 48 may be provided as hereinbefore explained, to by-pass any back voltages which might otherwise be applied to the igniters. Resistors 18 may be provided to limit the current through the low pressure gap 80.

When the condenser voltage reaches a predetermined value, the low pressure gap 60 breaks down, applying a positive voltage to either of the igniters 16 or TI, depending on which terminal of the condenser is positive. For example, the circuit may extend from one terminal of the condenser l1, through resistor 10, impedance 1|, rectifier device 46, resistor 18, gap 68, resistor 18, igniter 1T, mercury pool 15, induction coil 31, and conductor 32 to the other terminal of the condenser. This renders the valve means 12 conductive in a direction from the positive to nega-- tive terminal or from the mercury pool 14 to the mercury pool 15, thus discharging the condenser [1 through the coil 31 of the induction heating apparatus and charging the condenser I! in the opposite direction. The low pressure gap 68 breaks down again under the high frequency voltage produced, applying a positive voltage to the other of the igniters and rendering the switch device 12 conductive in the opposite direction. This sequence continues for successive high frequency oscillat ons produced by discharging the condenser I! through the inductive load circuit, maintaining a relatively high frequency load current through the induction winding 31 until the condenser voltage falls below the value required to break down the gap 68,. when the condenser will be recharged from the source. As the oscillatory discharges of the condenser are of a relatively high frequency, many such discharges may occur in a single half cycle of the source if the condenser is connected to the usual 60 cycle source. On the next half cycle the condenser will be charged in the reversedirection and a similar sequence results.

Referring to Fig. 5, the numerals 55 denote generally conductors connectedto a suitable source of alternating current energy. A switch device 18 may serve to connect'the condenser ll pacitative reactance of the condenser ll.

'Valve means 8i, comprising, for example, the

are discharge devices 28 and 48, which are connected in inverse relation may .be provided for connecting the condenser l1 and the primary winding iii of the welding transformer I2 as hereinbefore described; Suitable control means, such as the gaseous discharge devices 82 and 83, having anodes 84, 88, cathodes 88, 81, and control grids 88, 88 may be provided for applying control voltages to the igniters 28 and 48 of the arc discharge devices 20 and 48, respectively, to render them conductive.

Since the inductive reactance oi. the charging circuit for the condenser i1 is approximately half the capacitative reactance oi the condenser, the natural frequency of the charging circuit will be \/2 times the frequency of the source, and as a result the voltage wave of the condenser will be oscillatory in the general manner shown in Fig. 6, wherein the curve a indicates the fundamental voltage wave of the source and b indicates the voltage wave of the condenser. It will be seen that the voltage wave b of the condenser ll reaches successively higher peaks in the first several half cycles, each in excess of the voltage of the source. I

By rendering the gaseous discharge devices 82 and 83 normally non-conductive, and rendering them conductive only when the condenser voltage reaches a relatively high value, such as.indicated by the point e on curve 1) in Fig. 6, it is possible to obtain intermittent energization of the igniters 23 and 43 to render the arc discharge devices 20 and 48 conductive only, for example, on-every third half cycle of the condenser voltage wave. Intermittent discharges of the condenser of alternately opposite polarities may thus be provided, since the arc discharge devices 20 and 48 are rendered conductive only on odd spaced half cycles of the condenser voltage wave. They will conduct on positive and negative half cycles of the condenser voltage wave alternately, By thus using alternate positive and negative half cycles of the condenser voltage wave, saturation of transformer cores in the welding and/ or charging circuits is prevented, since the cores of any, transformers will be energized with substantially an equal number of positive and negative half waves during a given interval, thus preventing the production of a direct current component in either the charging or discharging circuits.

In order to render the gaseous discharge devices 82 and 83 normally non-conductive, so as to utilize this selective discharging of the condenser, means such as the batteries 88 and 9! may be provided for normally applying negative bias voltages to the control grids 88 and 89, respectively, of the devices. By utilizing a control resister 92 having adjustable contact members 83 and 94 to superimpose on the grids 88 and 88 a voltage proportional to the condenser voltage which is impressed between the cathodes 22 and 42 of the arc discharge devices, the voltage on the grids 88 and 89 may be varied in response to the voltage of the condenser l1. When the'condenser voltage reaches a suiliciently high value to overcome the negative bias voltage applied to' either of the grids by the batteries 88 or 8|, the

gaseous discharge device is rendered conductive.

and the arc discharge device controlled thereby conducts, connecting the condenser II to the primary winding I8 of the welding transformer.

When the condenser I1 is connected to the conductors 88 by closing the switch I8. the voltage across the condenser will vary generally as illustrated by the curve'b in Fig. 6. The batteries 88 and 8| normally apply negative bias voltages to the grids 88 and 88, respectively. rendering the gaseous discharge devices 82 and 88 non-conductive. An alternating current voltage proportional to the condenser voltage is superimposed on the grids 88 and 88. from the resistor 82, through the contact members 88 and 88, since the control resistor 82 is connected across the condenser I'I through the circuit extending from one terminal of the condenser through the conductor 82, primary winding I8 of the welding transformer I2, auxiliary inductance 88, rectifier device 48, battery 8I, control resistor 82, battery 88, igniter 28, cathode 22 and conductor 88 to the other terminal of the condenser I1. If the upper terminal of the condenser is'momentarily positive, the voltage drop in the resistor 82 renders the control grid 88 more negative, and overcomes the negative bias of the battery 8|, reducing the negative vo tage bias on the'control grid 88 sufliciently to render the gaseous discharge device 88 conductive. The condenser voltage is applied to the igniter 48 through the gaseous discharge device 88. and the arc discharge device 48 becomes conductive. The condenser I1 is dischar d through the primary winding I8 of the welding transformer I2 charging the condenser in the opposite direction. The aux liary condenser 85 passes sufficient of the high frequency osc llating discharge current to energire the igniter 23 and render the arc discharge device 28 conductive. An oscillatory discharge results. as hereinbefore descr bed. producing relatively large osc llatory welding currents during the remainder of the half cycle during which the discharge was initiated. Since the condenser volta e is not sufilciently high to overcome the negative bias voltage applied to the control grid 88 until the third halfcycle after the condenser I1 is discharged through the arc discharge device. 48. the arc discharge.

devices will both remain non-conductive during this interval after the high frequency oscillatory discharge. When the condenser voltage again reaches the predetermined value, this time in the negative direction, the negative bias on the control grid 88 of the gaseous discharge device 82'is overcome, and the arc discharge device 28 is rendered conductive to discharge the condenser in the opposite direction and effect a plurality of relatively high frequency discharges during a single half cycle of the condenser voltage. A plurality of intermittent oscillatory discharges of the condenser I! of opposite polarity may thus be obtained while the switch I8 remains closed.

Referring to Fig. 7, the reference numeral I8 may, as heretofore, denote generally a welding circuit including a welding transformer I2 having a secondary winding I3 for applying welding current to the work I I to be welded through the electrodes I5, and a primary winding I8. Suitable valve means 8| may be provided for connecting the primary winding I8 and the welding circuit I8 to the condenser II which functions as a source of welding energy.

In order to control the connection of the welding circuit I8 to the condenser II, the valve means may, for example, comprise a pair of are discharge devices 28 and 88 connected in inverse relation and controlled by gaseous discharge devices 82 and 88, respectively, in the manner hereinbefore described in connection with Fig. 5. For example, negative bias voltages may be applied to the control grids 88 and 88 of the gaseous discharge devices by means, such as the batteries 88 and 8|, to normally render the gaseous discharge devices 82 and 88 non-conductive. In order to render the gaseous discharge devices 82 and 88 selectively conductive in response to predetermined voltage conditions of the condenser I I, means may be provided for superimposing on the control grids 88 and 88 a voltage proportional to the voltage of the condenser such as, for example, the control resistor 82. As hereinbefore described in connection with Fig. 5, the control voltage will be superimposed on the control grids -88 and 88 by means of the control resistor 82, making one or another of the control grids pod- -tive. or reducing the negative bias voltage thereof sumciently to render the gaseous discharge device conductive, dependingonthe instantaneous polarity of the voltage across the condenser II.

In order to provide for connecting the condenser I! to a suitable source of alternating current, such as, for example, the alternattor 88. suitable switch or valve means may be provided comprising, for example, the inversely connected arc discharge devices 88 and 88, having control electrodes or igniters 81 and 88, respectively.

With a view to connecting the condenser I1 to the source 88 intermittently, or periodically to effect intermittent or periodic welds, suitable timing means, denoted generally by the reference numeral I88, may be provided. The timing means may be of any suitable type adapted to effect a synchronous connection of the condenser I1 to the source 88 and may, for example, comprise substantially the arrangement shown and described in detail in Patent No. 2,081,987, Serial No. 59,402, issued to John W. Dawson on June 1, 1937, and assigned to the Westinghouse Electric & Manufacturing Company, the assignee of this application.

The timing means I88 may, for example, comprise gaseous discharge devices IN and I82 for selectively applying control voltages to the igniters 81 and 88 of the arc discharge devices 85 and 86 respectively to render them conductive selectively. The gaseous discharge devices I8I and I82 may be provided with control grids I88 and I84, respectively, which may be connected to suitable sources of negative bias voltage such as, for example, the rectifier bridge circuits I85 and I86 Interposed between the sources of bias voltages and the control grids are windings I81 and I88, respectively, which may be positioned on a magnetic core member I88 having an air gap I I8 therein. A disk member I I2 may be provided having a plurality of pins II8 of magnetic material positioned around the periphery thereof in spaced relation, and adapted to pass through the air gap II8 when the disk H2 is rotated. Suit able means such as the synchronous motor III, which may be energized from the source 88 may be provided for driving the disk II2.

Rotation of the disk effects variations in the magnetic reluctance of the air gap H8, inducing voltage pulsations in the windings I81 and I88 which alternately add to and subtract from the negative bias voltages applied to the controigrids I83 and I84 by the rectifier bridge circuit I88 and I88. The gaseous discharge devices IN and I82 may thus be rendered conductive periodically or intermittently by means of the potitive voltage impulses at any suitable intervals, by varying the spacing of the magnetic pins II 3 on the disk H2.

In order to control the particular point in the different cycles, at which the arc discharge devices 95 and 38 are rendered conductive, phase control means denoted, generally, by the numeral II8 maybe provided. For example, gaseous discharge devices H1 and H8 having control grids I I3 and- I20, respectively, may be utilized to shunt control resistors I2I and I2Ia which normally limit the current to the igniters 31 and 38 of the arc discharge devices 35 and 30, respectively, to prevent the gaseous discharge devices I and I02 from rendering them conductive until predetermined variable points in each cycle for which the gaseous discharge devices MI and I02 are.

rendered conductive.

The gaseous discharge devices H1 and H8 may, for example, be controlled by applying suitable bias voltages to the control grids I I3 and I through control transformers I22 and I23, respectively. In order to provide for varying the phase of the voltages applied to the control transformers I22' and I23 with respect to the.

voltage of the source 33, a phase shifting circuit I24 may be provided. The phase shifting circuit I24 may be energized from a transformer I25 connected to the source 33 and having a secondary winding I21 provided with a center tap I28. An impedancenetwork may be provided by connecting a voltage divider resistance I across the secondary winding I21, and connecting an impedance i 3| across a portion of the resistance. The phase shifting circuit I24 may be connected to the control transformers I22 and I23 by means of a variable tap I32 on the resistance I30 and a variable tap I34 connected between the center tap I28 of the control transformer I25 and a balancing resistance I38 connected between the control transformers I22 and I23.

By connecting a suitable inductance I38 between the source 33 and the condenser I1 having an inductive impedance equal to approximately one-half of the capacitative impedance of the condenser I1, an oscillatory charging circuit may be provided for the condenser I5, as illustrated by the voltage curves of Fig. 6. By thus selecting the value of the. impedance I38 with respect to the condenser I1, there will be produced a component of the condenser charging current having a. frequency equal to the square-root of two times the frequency of the source. Under these conditions, as shown by the curves in Fig. 6, the resultant condenser voltage will have a frequency difi'ering from the voltage of the source, and will reach successively higher peak values until a maximum is attained on the third half cycle after the condenser is connected to the source. Since the values and the manner of fluctuation of the condenser voltage relative to the voltage of the source vary, depending on the point at which the condenser is connected to the source with respect to the voltage wave of the source, it will be seen thatthe phase shifting means H8 is important in securing the proper relations between the condenser and source voltages to achieve'the desired conditions.

By properly selecting the relative values of the negative bias voltages applied tothe control grids 88 and 83 of the gaseous discharge devices 82 and 83, and the voltages applied thereto by the control resistor 32 in response to the instantaneous voltage of the condenser I1, it will be possible with Figs. 5 and 6. By thus spacing the welding impulses, intermittent high frequency welding impulses may be effected without producing any direct current component in either the charging or the welding circuit. By varying the phase relation, the energy charge of the condenser may be varied and heat control of the welding operation obtained. Also the effects of the relatively high frequency condenser discharges on the source may be minimized by connecting the condenser to the welding circuit at a point near the zero point of the voltage wave of the source.

Referring to Fig. 8 of the drawings, the reference numeral I0 may, as heretofore, denote, generally, a welding circuit which may be connected to the condenser source of welding energy I1 by switch means I40 for effecting welding operations of varying durations. The condenser I1 may be connected for chargin to the conductors 55 which may be connected to a suitable alternating current source. The switch means I40 may comprise a pair of inversely connected valves or are discharge devices 20 and 40 controlled by gaseous discharge devices 82 and 83, respectively, which may be normally rendered non-conductive by means of negative bias voltages applied to the control grids 88 and 83 thereof by means such as batteries 30 and 3|, in the manner hereinbefore described in connection with Figs. 5 and 7. A control resistor 32 may be provided as therein described for superimposing on the control grids 88 and 83 positive voltages effective to reduce the negative bias voltages to suii'iciently low values to render the discharge devices 82 and 83 conductive selectively. For a purpose hereinafter set forth, the resistor 32 may comprise separate sections 32a and 321), instead of a single section as in Fig. 5.

In order to provide for rendering the discharge devices 82 and 83 conductive only for predetermined timed intervals, which may be selected by the operator, suitable timing means I42 mayv be provided for controlling the connection of the resistor sections 92a and 92b. For example, switch devices I43 and I44 may be provided, having normally closed and normally, opened contact members M311 and H411 between the sections 32a and 32b, and operating windings I45 and I48, respectively. The operating winding I46 may be connected to the rectifier bridge circuit I41 di-- rectly', while the operating winding I45 may be connected thereto in series circuit relation with a control valve I48 having an anode I43, a control grid I50 and a cathode I5I, which maybe energized from any suitable source of electrical energy. A control switch I52 may be provided for connecting the rectifier bridge circuit I41 to a suitable source of alternating current to initiate a welding operation, such as, for example, the control transformer I53, which may be connected to the conductors 55.

In order to provide for a predetermined timed welding interval, the control grid I50 of the control valve I48 may be connected'to the rectifier bridge circuit through a resistor I55 which provides a negative bias voltage between the control current flow through the resistor I55 being, for

the welding operation.

. which are negative with respect to the condenser example, connected in shunt circuit relation therewith by means of a movable contact Ill and a control resistance Ill.

when the control switch III is closed, the rectifier bridge circuit I" is immediately energized and the control switch Ill operates, closing con-- tact members Illa to connect the sections 02a and 02b of the control resistor 92 between the control electrodes or igniters II and ll of the arc discharge devices ll and M, so that the voltage or the condenser ll is impressed thereon. A voltage proportional to the voltage of the condenser ll is thereby superimposed on the control grids ll and ll through the contact members It and Il in the manner heretofore described in connection with Fig. 5, and the arc discharge devices 20 and ll may be rendered conductive in response to predetermined voltage conditions 0 the condenser l'l.

As soon asthe rectiiler bridge circuit I" is connected to the source, plate voltage is applied to the plate ill of the valve Ill, and a limited current flows through the circuit from the positive terminal .of the bridge circuit, operating winding Ill of the control switch ilt, plate or anode Ill of the valve device Ill, cathode Ill, and control resistance ill to the negative terminal of the rectifier bridge. A voltage is thus produced across the resistor Ill which charges the condenser I" through the resistor Ill, making the cathode ill positive with respect to the control grid III]. which prevents the valve ill from passingjsuflicient current to operate the control switch Ill.

As soon as the condenser Ill becomes charged, the current flow through the control resistor III ceases, and the negative bias voltage on the control grid I" is removed. Thecontrol valve ill then becomes suillciently conductive to operate the control switch Ill, opening contact members Illa to disconnect thesections oi the control gaseous discharge devices .2 and N are thus re- 4 turned to the non-conductive state, terminating Referring particularly to Fig. 9, it will be seen that the welding circuit III is disposed to be connected to-the condenser 11 by a pair of inversely connected arc discharge devices 20 and l0 under the control of gaseous discharge devices I! and 83 arranged in a manner similar to that hereinbefore described in connection with Figs. 5, 7 and 8.

In order to control the conductivity of the gaseous discharge devices I! and 88 to initate welding operations, suitable means may be provided for normallyv applying alternating current bias voltages to the control grids l8 and 89 thereof,

voltages on their respective arc discharge devices.

For example, a control transformer I80 may be provided, having a primary winding Ill connected to the source of alternating current from which the condenser I1 is energized and secondary windings ill and Ill which may be connected between the cathodes ll, 01 of the gaseous discharge devices and the respective control grids II, It thereof. With a view to varying the point 70 voltages applied to the control grids ll and ll 7s from the secondary windings Ill and ill, respectively.

In order to control the conductivity of the gaseous discharge devices I! and I3, selectively in response to the high frequency oscillations produced in the discharge circuit between the condenser and the primary winding i l of the welding transiormer ll, subsequent to the initiation of a welding operation by either of the Baseous discharge devices 02 or ll, suitable means may be provided for applying control bias voltages to the' control grids II and ll independently of the source. For example, an auxiliary variable condenser Ill and a control resistor I may be connected by means of movable contacts I and H0 to control resistors ill and I1! in the grid circuits to provide a relatively low impedance path between the cathodes I2 and l! for the relatively highfrequenc oscillations produced in the discharge circuit, and apply bias voltages to the control grids I0 and It to render the discharge devices I! and ll selectively conductive in response to variations of voltages in the discharge circuit. A low pressure gap device a ll: may be'connected between the control grids ll and It to act as a protective device for the circuit and bypass any excessively high voltage surges which may be introduced into the control grid circuits.

' Iclaim:

' Referringto Fig. 10, the curve it represents the voltage wave of the source of the system of Fig. 9, while the curve 0 represents the voltage of the condenser I'I which is connected to the source for charging. The curves 1 and g represent different values of negative bias voltage applied to theone or another of the-control grids 88 or 89 by the secondary windings II! or Ill of the control transformer ill. The curve It represents the minimum value of negative bias voltage with respect to the condenser voltage e which is eifective to render either of the gaseous discharge .devices 82 or II non-conductive. It will be seen that whenever the condenser and source voltages are positive with-respect to either of the dischargedevlces I! or II, the bias voltages are negative and normally prevent the devices from conducting. when the curves f and a intersect the curve h, the gaseous discharge device 82 or ll is rendered conductive to initiate a welding operation. By adjusting the movable contact memhers I" and Ill to vary the value of the bias voltage applied to the control grid 88 or 88, as represented by the curves I and a. the points of intersection z and i! of the negative bias voltages with the minimum negative bias voltage curve h may be changed,'so as to occur at different intervals with respect to the horizontal or time axis. Accordin ly. the point at which the arc discharge devices 2|! and 40 are rendered conductive may be varied with respect to the source and condenser voltage waves illustrated by the curves d and e by varying the negative bias voltages applied to the control grids l8 and 89.

.Referring to Fig. 11, the curve e denotes the condenser voltage wave, while the curve d indicates the voltage wave of the source. The curves 1 and m indicate diilerent conditions of negative bias voltages applied to the control grids B8 or 88 from the secondary windings II! or I" of the control transformer I under diiferent predetermined conditions. By varying the current through the condenser Ill and making the condenser lll suihciently large and the resistors in series therewith sumciently small. an appreciable guano voltage drop in the grid resistances Ill and I12 may be produced during the charging period of the condenser I61 through the circuit extending from the igniter 23 through conductor I16, secondary winding I62, contact member I66, resistor "I, contact member I69, condenser I61, resistor I68, contact member I10, resistor I12, contact member I66, secondary winding I63, and conductor I16 to igniter 63. The condenser current being a leading current, the voltage drop produced in the grid resistors Ill and I12 thereby will be out-oi-phase with the voltage or the secondary winding I62 or I63. Accordingly, the resultant bias voltage indicated by the curve m, which illustrates the bias voltage when the condenser I6'I is relatively large, will be out-of-phase with the normal bias voltage produced by voltage secondary winding I62 or I63, denoted by the curve I. As a result, the intersection of the negative bias voltage with the minimum bias voltage curve It will be advanced by increasing the capacity of the condenser I61. The point at which the gaseous discharge devices 62 and 83 are rendered conductive with respect to the condenser voltage wave e may thus be altered. Phase control of the firing points of the arcdischarge devices 26 and 66 with respect to source or the condenser voltage wave may thus be obtained by either adjustment of the movable taps I65 and I66, the size of the condenser I61, or of the movable taps I66 and I16.

During the discharge period, current from the supply flows from the source through the arc discharge devices 62 and 83, adding algebraically to the current oscillations in the discharge or welding circuit. It may happen that, when the high frequency oscillations in the discharge circuit are dying out, there is insufilcient potential across the condenser I1 to permit the current in the arc discharge devices to drop to zero and allow them to deionize. The supply current may continue to flow in the inductive discharge circult and may not reverse until late in the next half cycle. The condenser I1 remains connected to the welding or discharge circuit and is partially short-circuited, so that it cannot charge properly on the succeeding half cycle. or sufllclent grid bias voltage may oe produced to permit one or the other or the gaseous discharge devices to conduct and render one or the other of the arc discharge devices conductive prematurely.

In order to prevent the occurrence of such conclitions, the system of Fig. 9 may be modified to insure the gaseous discharge devices and arc discharge devices being rendered non-conductive whenever the condenser voltage drops below a predetermined value. 8

Referring to Fig. 12, it will be seen that the arrangement of the arc discharge devices 20 and 46 for connecting the welding circuit I0 to the condenser I1 is substantially the same as shown in Fig. 9. In order to provide for insuring that the gaseous discharge devices 82 and 63 will be rendered non-conductive as soon as the voltage in the discharge circuit of the condenser I1 drops tc a predetermined value, regardless of the bias voltages produced by the control transformer I60, suitable means, such as the rectifier bridge circuits I11 and I16 may be provided for applying fixed negative bias voltages to the control grids 88 and 86, respectively, to render them negative when the voltages applied thereto from resistors I19 and I86 proportional to the condenser voltage are below a desired value so that I89 and I90 conduct 18 the gaseous discharge device will be maintained non-conductive on any condenser voltage below that by which they may be readily controlled.

Means, such as the switch I62, may be provided for connecting the resistors I19 and I to provide a bias circuit extending from one terminal of the condenser I1 at igniter 23, through conductors I83 and I64, rectifier device I11, conductor I66, resistor I16, contact members I820, resistor I60, conductor I66, rectifier device I16, conductors I81 and I88 to the igniter 43 and the other terminal of the condenser I1. Rectifier devices I99 and I provide unidirectional shunts to connect the grids 88 and 69to contact members I92 and I93 of the resistors I18 and I80, respectively, whenever the voltage of the condenser I1 drops below the predetermined value in any cycle. Regardless of the bias voltages applied to the grids by the secondary windings I82 and I83 in any half cycle of the source voltage wave, the voltage ofthe grids cannot be greater than the voltages at the contact members I92 and I93, and will be negative when these voltages drop below the predetermined value.

Referring to Fig. 13, the curve It denotes the variation in the voltage of the contact members I92 and I93 with the condenser voltage, while the curve 2' represents the minimum negative grid voltage necessary to prevent the gaseous discharge devices from becoming conductive, for different values of condenser voltage. The/devices conduct at points above and to the right of the curve i, but in the system of Fig. 12 points below and to the right of the curve 1 do not exist. The intersection of the two curves, therefore, represents the lowest value of condenservoltage at which the gaseous discharge devices can be rendered conductive, which point may be varied by adjustment of the movable contact members I92 and I93. If the grid voltage tends to become positive at low condenser voltages, the rectifiers and lower the grid voltage to that at the movable contact I92 or I93. The devices 82 and 83 are under these conditions rendered non-conductive, regardless of the bias voltages produced by the secondary windings I62, I63, so that the condenser I1 is disconnected from the welding circuit l0 and recharges from the source.

Referring to Fig. 14, the reference numeral 36 denotes, as heretofore, a load, comprising, for example, induction heating apparatus including an induction coil 31 and a cupola 38, which is disposed to be connected to a condenser I1, connected to a suitable source of alternating current energy bymeans of a current limiting charging iinsipedance 69, a transformer I66, the conductors A pair of inversely connected arc discharge devices 20 and 40 controlled by gaseous discharge devices 82 and 83, respectively, are disposed to control the connection of the condenser I1 to the induction coil 31. In order to provide for normally rendering the gaseous discharge devices 62 and 83 non-conductive, suitable means may be provided for applying negative bias voltages to the control grids 88 and 89 thereof, such as, for example, the rectifier bridge circuits I66 and I91 which may be energized from the conductors 65 through a suitable control transformer I98, and grid resistors I99 and 200, respectively.

In order to provide for rendering the discharge devices 82 and 83 conductive and varying the point at which they are rendered conductive with respect to the voltage wave of the condenser I'I,

. I9 suitable means, such as the phase-shifting circuit "I, may be provided for applying alternating current bias voltages to the control grids II. and 89 to overcome the negative bias voltages applied thereto by the rectifier bridge circuits Ill and ill. The phase-shifter circuit may. for example, comprise an impedance network including a resistor 20! having an impedance "I connected in shunt circuit relation with a portion thereof and connected across the secondary winding 2 of a transformer 20!, the primary winding 20! of which may be connected across the condenser l'l. Means, such as the control transformers 201 and 208 may be connected between a movable tap 209 on the control resistor 202 and an adjustable tap 2m connected to a center tap iii of the secondary winding 204 and engaging a balancing resistor 2|! to impress bias voltages en the control grids 88 and 88 in response'to variations of the condenser voltage. In order to provide for maintaining the gaseous discharge devices 20 and conductive after a current impulse has been initiated, suitable menas may be provided for applying control voltages to the igniters 23 and ll, thereof,

such as, for example, the current transformer it which may be provided with secondary windgs ill and Ill, respectively, connected between igniters and cathodes of the arc discharge devices 20 and 40, respectively. Means, such as the rectifier devices 2", may be provided in series circuit relation with the secondary windings 2|! and III to prevent reverse voltages being applied to the igniters of the arc discharge devices. Condensers Ill may be provided to regulate the time or phase relation of the current to the igniters.

The welding circuit illustrated in Fig. 14 functions generally in a manner similar to the other heating and circuits hereinbefore described. The negative bias voltages applied to the control grids 88 and 88 from the rectifier bridge circuits I" and I81 normally render the gaseous discharge devices non-conductive. When the condenser voltage reaches a predetermined value, voltage impulses are superimposed on the control grids through the phase-shifting circuit II, the control transformers I01 and 208, which are suii'icient to render the gaseous discharge devices selectively conductive depending on the polarity of the voltages applied. When either of the arc discharge devices. for example, the device 20, is rendered conductive by its associated gaseous discharge device, the condenser i1 is discharged through the induction coil 31, setting up a relatively high frequency oscillating current therein. Subsequent firing of the arc discharge devices 20 and 40 is effected by voltages applied to the igniters 23 and 43 from the control transformer 2 in response to the flow of a high frequency current through the induction coil 31 from the condenser i1, thus providing a relatively high frequency oscillating heating current in the material in the cupola 88. The initiating point of the arc discharge devices may be varied with respect to the voltage wave of the condenser II by means of the phase-shifting circuit I, as desired.

From the above description and the accompanying drawings, it will'be realized that we have provided in a similar and effective manner for producing relatively high frequency oscillating welding or heating currentsby selectively connecting a condenser, which is connected to a suitable source of electrical energy, to a welding or heating circuit. Relatively large amounts of heat energy may thus be produced by the discharge of the condenser in a relatively short period. since the condenser is connected to the source through an impedance which limits the flow of current from the source, little or no energy is supplied to the load circuit directly from the source. Substantially no fluctuations in the source system are produced when the welding circuit is connected to the condenser in the manner we have described. Where the invention has been described as suitable for producing a plurality of relatively high frequency oscillatory discharges for each charging of the condenser I! from the source, as in the systems shown in and described in connection with Figs. 3, 4, 5, '7, 8, 9, it will be apparent that these systems may also be used for supplying only a single discharge impulse for each charging of the condenser l'l from the source, by merely omitting the auxiliary capacitor 45 and making the gap devices 60 and Ill such that they will not break down at the lower value of voltage to which the condenser l1 may recharge due to the oscillatory nature of the discharge circuit, as is clearly described in connection with the system of Fig. 3.

The principles of our invention may also be applied to arc welding. In such an event, the material to be welded and the welding electrode are connected to the terminals to which the primary of the welding transformer is connected in the various illustrated embodiments of our invention (e. g., the Fig. 5 modification). In addition, an impedance, such as a capacitor or a resistor, is connected across the terminals to prevent the discharging network for the capacitor from becoming electrically isolated from ground when the welding arc breaks.

Since certain changes may be made in the above description and different embodiments of the invention may be made, without departing from the spirit thereof, it is intended that all the matter contained in the above description or shown in the accompanying drawings shall be considered as illustrative and not in a limiting sense.

We claim as our invention:

1. A power system comprising, a condenser, a resonant charging circuit connecting the condenser to a source of electrical energy to produce an oscillating charging current of a relatively low frequency, a separate discharging circuit including an inductive load device, valve means having control electrode means operable to connect the discharging circuit to the condenser to produce a relatively high frequency oscillatory discharge of the condenser through the inductive load device, and means including a control circuit energized in accordance with the charge of the condenser to control the energization of the control electrode means for controlling the operation of the valve means.

2. An energy translating system comprising, an inductive load device, a condenser for supplying reiatively high frequency impulses of electrical energy to the load device, circuit means connecting the condenser to a source of relatively low frequency alternating current including an inductance to provide an oscillatory charging circuit having successively increasing peak voltages in excess of the source voltage, and valve means having a control electrode energized in response to a predetermined condenser voltage in excess of the source voltage operable to connect the condenser to the load device at spaced intervals.

3. Apparatus for supplying relatively highfrequency electrical energy to'an inductive load cir- 9,478,9 Ill cuit comprising, a condenser, circuit means connecting the condenser to a source of electrical energy, a. pair of inversely connected arc discharge devices having control electrodes operable to connect the ;;condenser to the load circuit, andcontrol meanssincluding control valve means energized from the condenser adjustable for applying diflerent control voltages to one of the control electrodes to render its associated are discharge device conductive at different predetermined points in the condenser voltage wave.

4. The combination with an inductive load circult and a condenser "connected to a source of charging circuit havin successively increasing peak voltages, a load circuit including sumcient inductance to provide a relatively high natural circuit frequency, are discharge means operable to connect the load circuit to the condenser, con.- trol means for said are discharge means, circuit a means for applying a control voltage to the-concondenser voltage, and an auxiliary condenser connected to apply a relatively high frequency control voltage to the control electrode from the load circuit to render the devices conductive in response to oscillations in the load circuit.

5. A switching system for a relatively high frequency load circuit including a source of electrical energy, a condenser connected thereto for energization and an inductive circuit device comprising, a pair of inversely connected gaseous discharge devices having control electrodes to render them conductive connected between the condenser and the inductive circuit device in back-to-back relation, circuit means for applying a voltage to the electrodes in response to a predetermined condenser voltage to initiate the conductivity of one of the devices, and control means including an auxiliary condenser connected to provide a control voltage to the control electrodes in response'to relatively high frequency oscillations in the load circuit to render them conductive after the load circuit has been connected to the condenser.

6. The combination with a condenser connected to a source of electrical energy and an inductive load circuit, of bi-directional valve means having control electrodes operable to connect the inductive load circuit to the condenser, circuit means for applying a control voltage to the control electrodes in accordance with a predetermined condition of the condenser to set up high frequency oscillations between the condenser and .the load circuit, and means including a condenser connected between the control electrodes to provide a relatively low impedance energizing circuit for applying the relatively high frequency voltage to the control electrodes.

7. The combination with an inductive load circuit and a condenser disposed to be energized from a source of electrical energy, of impedance means to limit the flow of energy from the source, a valve means for connecting the condenser to the load circuit, control means operable to apply a control voltage to the valve means, and means responsive to the rate of charging of the condenser for rendering the said control means inoperative until the condenser voltage reaches a predetermined value.

8. An intermittent load energizing system comprising a condenser source of current, circuit means including inductance for connecting the condenser to a source of'alternating current of relatively low frequency to provide an oscillatory trol means in response to the condenser voltage to render the arc discharge means selectively conductive, said circuit means being capable of adjustment'to render the arc discharge means conductive only 'in response to predetermined condenser peak voltages higher than preceding voltage peaks to effect timed discharges of the condenser, and means for varying the point onthe voltage wave of the source at which the condenser is connected to the source.

9. A power system comprising, a, condenser source of electrical energy connected to a source of alternating current, an inductive load circuit, inversely connected arc discharge valve means having control electrodes operable to connect the load circuit to the condenser, gaseous discharge means operable to apply control voltages to the control electrodes to render the arc discharge valve means conductive, control means for the gaseous discharge means, circuit means for applying alternating-current bias voltages to the said control means in opposition to the condenser voltage applied to the associated arc discharge valve means, means to vary the bias voltages to initiate conductivity of the arc discharge means at diiferent predetermined points in the condenser voltage wave, and an auxiliary condenser connected between the control means to render the gaseous discharge means conductive in response to relatively high frequency oscillations in the load circuit.

10. A power system comprising, a load circuit including a predetermined amount of inductance, a condenser, circuit means for connecting the condenser to a source of electrical energy for charging, arc discharge valve means for connecting the load circuit to the condenser to effect a rapid discharge thereof and produce relatively high frequency oscillations in the load circuit, control means for the arc discharge valve means, circuit meansto apply a control voltage to the control means to render the valve means conductive, and an auxiliary condenser connected to apply'a relatively high frequency control voltage to the control means from the welding circuit to render the valve means conductive subsequent to initiation in a given half cycle of the source voltage wave.

11. An impulse energy system comprising, a condenser, an oscillatory charging circuit having an inductive impedance approximately one half the impedance of the condenser for connecting the condenser to a relatively low frequency source of electrical energy, a load circuit containing a predetermined amount of inductance to provide a relatively high natural circuit frequency and produce an oscillatory discharge of the condenser at a relatively high frequency, a pair of inversely connected arc discharge devices for connecting the load circuit to the condenser, said devices having control electrodes for rendering the devices conductive, control means responsive to a predetermined condenser voltage to energize one of the control electrodes to render its associated arc discharge device conductive, and circuit means including an auxiliary condenser connected to the load circuit to pass a relatively high angers condenser to the load circuit, circuit means for v applying a control voltage to the control electrode of one of the valve means to initiate the connection of the load circuit to the condenser in predetermined relation to the condenser voltage wave to produce a relatively high frequency load current, means for producing a relatively high frequency control voltage bypass between the control electrodes to selectively render the valve means conductive alternately during the remainder of the half cycle of the condenser voltage wave, and circuit means to render the valve means non-conductive when the condenser voltage reaches a predetermined minimum value.

13. A switching system for connecting a condenser disposed to be charged from a suitable source-of electrical energy to a load circuit having a relatively high natural frequency comprising, valve means connected between the condenser and the load circuit, control means for the valve means, means for applying restraining voltages to the control means to render the valve means non-conductive, circuit means for applying to the control means a voltage proportional to the voltage of the condenser to initially render the valve means conductive under predetermined conditions, and an auxiliary condenser for supplying a relatively high frequency control voltage to the control means subsequent to the valve means being initially rendered conductive to effect selective connection of the load circuit to the condenser during the remaining portion of the half cycle in which the connection was initiated.

14. The combination with a stored energy device connected to be charged from a source of alternating current and valve means having control means for controlling the connection of the stored energy device to a load device to provide a load circuit having a relatively high natural frequency, of means for'applying an alternatingcurrent bias voltage to the control means from the source to render the valve means 'non-conductive until a predetermined point relative to the voltage wave of the source. and means to vary the point at which the valve means is rendered conductive.

15. In'combination with valve means having control means to render the valve means conductive to connect a load circuit having a relatively high natural frequency to a condenser itor, a pair of electric discharge valves each havsource of stored electrical energy energized from a relatively low frequency source of alternating current, of circuit means for applying an alternating-cu'rrent bias voltage to the control means to prevent the. valve means for becoming conductive until a predetermined point in a given half cycle, and an auxiliary condenser to vary the phase of the bias voltages relative to the voltage of the source.

16. The combination with a load circuit having a relatively high natural frequency and a .pair of unidirectional valve devices with control .s 24 ductive, circuit means for applying bias voltages to the control electrodes in opposition to the voltages applied to the respective valve means from the source to maintain the valve means selectively non-conductive until predetermined points of the voltage wave, and means including an auxiliary condenser connected to provide a relatively low impedance path through the circuit'means for a relatively high frequency control current from the load circuit to render the control means selectively conductive in response to relatively high frequency oscillations produced in the load circuit when the connection of the load circuit to the source is initiated.

17. Th combination with valve means havin control means energizable to render the valve means conductive to connect a condenser disposed to be changed from'a relatively low frequency source of electrical energy through a current limiting impedance to a load circuit having a relatively high natural frequency of oscillation, of control valve means having control electrodes to control the energization of the control means, means for applying alternating-current control voltages to the control electrodes responsive to the voltages applied to their respective valve means but of opposite phase, circuit means for applying control voltages to the control electrodes in response to the condenser voltag and in generally the same phase relation therewith, additional circuit means for applying substantially constant negative bias voltages to the control electrodes, and unidirectional current means connecting the control electrodes to the said circuit means to provide one way shunts to reduce voltage on the control electrode to a predetermined value to deenergize the control means whenever the condenser voltage reaches a predetermined minimum value.

18. Converting apparatus comprising a capacitor, an inductor, means for charging the capacing a pair of main electrodes and a control electrode connected with the main electrodes in antiparallel between the capacitor and the inductor for discharging the capacitor through the inductor, and circuit means eflecting energization of the control electrodes in accordance with the capacitor voltage.

19. Converting apparatus comprising a capacitor, an inductor, periodic current means connected for charging the capacitor to successively opposite polarities, and a pair of electric discharge valves each provided with a pair of main electrodes connected in anti-parallel between the capacitor and the inductor for discharging the capacitor through the inductor, said capacitor, inductor and valves constituting a series tuned network tuned to a frequency substantially higher than that of said periodic current means.

20. For use for supplying current to the primary of a transformer having a load circuit in terposed in the secondary, a condenser, circuit means connecting the condenser to a source of current for alternately charging the condenser to opposite polarities from the source, and additional circuit means includinga pair of electric discharge valves interposed in anti-parallel between said condenser and said primary to provide an oscillatory discharge of said condenser.

21. Converting apparatus comprising a capacitor, an inductor, means for charging the capacitor, a pair of electric discharge valves each having a pair of main electrodes and a control electrode connected in anti-parallel between the inductor, and an auxiliary capacitor connected between the control electrodes to provide an energizing circuit.

22. A control circuit for valve means having control means to render the valve means conductive to connect a load circuit to a condenser source of stored electrical energy energized from a relatively low frequency source of alternating current comprising, circuit means for applying a bias voltage to the control means to render the valve means non-conductive until a predetermined point in the voltage wave of the source, and control means associated with the circuit means for varying the point in the voltage wave of the source at which the valve means is rendered conductive.

23. Converting apparatus comprising, a capacitor, an inductor, means for charging the capacitor, a pair of electric discharge valves each having aa pair of main electrodes connected in anti-parallel between the capacitor and the inductor and a control electrode energizable to render the valve conductive for discharging the capacitor through the inductor, and means for efiecting energization of one of the control elecreaches at least a predetermined value.

24. In a system for supplying power to a re active load circuit, the combination of an energy storage device chargeable to either of two opposite polarities, circuit means coupling said device to said circuit so as to enable the device when charged to either polarity to supply energy to the circuit and to enable reactive energy stored in the circuit to be returned and partially recharge the device to the opposite polarity, and additional circuit means coupling said device to a source of alternating current power so as to complete the recharging thereof to either of said opposite polarities.

25. In a system for supplying power to a reactive load circuit, the combination of an energy storage device chargeable to either of two opposite polarities, circuit means coupling said device to said circuit so as to enable the device when charged to either of said polarities to supply energy to the circuit and to enable reactive energy stored in the circuit to be returned to and partially recharge the device to the opposite polarity, and additional circuit means coupling said device to a source oi alternating current power so as to complete the recharging thereof to each of said opposite polarities alternately,

28. In a system for supplying power to aload circuit, an energy storage device, means for supalternating current for charging to opposite polarities in accordance with the alternating polarity of the source frequency, and means including a pair of inversely connected electrodecontrolled valve devices for connecting the condenser to the primary circuit of the transformer in accordance with a predetermined condition of charge of the condenser in any one half cycle of charging for discharging the condenser through the primary circuit within said half cycle of the source frequency.

' JOSEPH SLEPIAN.

ALFRED B. WHITE.

REFERENCES CITED The following reierenices are of record in the file of this patent:

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